The present invention relates to flat panel display devices and more particularly flat panel electroluminescent display devices. In such devices an X-Y array of display elements or cells, are provided upon an insulated substrate, and are interconnected together to produce a large area flat panel display which is substitutable for a cathode ray tube. Each of the display elements of the array comprises integral thin film transistor switching and control circuit elements, which are used to selectively address specific areas of the planar electroluminescent phosphor layer which is excited to produce light output in a display pattern.
Such an electroluminescent display panel is described in U.S. Pat. No. 4,042,854 entitled, "Flat Panel Display Device With Integral Thin Film Transistor Control System." As described in the copending application, the electroluminescent display panel is fabricated by vacuum depositing sequential layers of selected materials to form the X-Y array of display elements on an insulative substrate. Each display element covers an equal area of the panel, and a substantial portion of the area of the display element is occupied by the individual thin film circuit elements and particularly by the requisite spacing between such elements to prevent unwanted electrical interaction between the elements. For high resolution applications the physical size and area of this display element must be reduced, and this further increases the percent area of each display element taken up by the thin film circuit elements as opposed to the electroluminescent electrode. This electrode is the only portion of the display element which actually excites the electroluminescent phosphor which is disposed uniformly over the panel. The actual size of the thin film circuit elements cannot readily be reduced because of the need to maintain desired electrical characteristics. This is particularly true with respect to the storage capacitive element which is required in one embodiment of the addressing circuit utilized for such an electroluminescent display panel. In order to achieve a large enough capacitive value for this storage capacitor, its effective area is relatively large.
In the above described copending application, a technique for effectively isolating the electroluminescent phosphor layer from the thin film circuit elements and the drive signal buses is set forth. A laminated photopolymerizable layer is provided over such thin film circuit elements and the signal buses to thus effectively isolate the electroluminescent phosphor from these electrical components. This laminated photo-polymerizable layer is applied in a relatively thick layer with the photo-polymerizable insulative layer being selectively removed from the areas over the electroluminescent electrode to permit contact of such electrode with the phosphor layer which is then deposited over such electrodes and over the insulative polymerized portions which cover the thin film circuitry and signal bus elements.
The brightness and resolution of such electroluminescent display panels has been limited by the effective area of the electroluminescent phosphor layer which is in contact with and excited by individual electroluminescent electrodes. Till now this lit area has been about fifteen percent of the panel area. It is, therefore, highly desirable that the electroluminescent electrodes be extended to cover a greater area of the total panel area.